/*
 * Copyright (c) 2000, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
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 *
 */

package javax.imageio.spi;

import java.io.Serializable;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

/**
 * A node in a directed graph.  In addition to an arbitrary
 * <code>Object</code> containing user data associated with the node,
 * each node maintains a <code>Set</code>s of nodes which are pointed
 * to by the current node (available from <code>getOutNodes</code>).
 * The in-degree of the node (that is, number of nodes that point to
 * the current node) may be queried.
 */
class DigraphNode implements Cloneable, Serializable {

  /**
   * The data associated with this node.
   */
  protected Object data;

  /**
   * A <code>Set</code> of neighboring nodes pointed to by this
   * node.
   */
  protected Set outNodes = new HashSet();

  /**
   * The in-degree of the node.
   */
  protected int inDegree = 0;

  /**
   * A <code>Set</code> of neighboring nodes that point to this
   * node.
   */
  private Set inNodes = new HashSet();

  public DigraphNode(Object data) {
    this.data = data;
  }

  /**
   * Returns the <code>Object</code> referenced by this node.
   */
  public Object getData() {
    return data;
  }

  /**
   * Returns an <code>Iterator</code> containing the nodes pointed
   * to by this node.
   */
  public Iterator getOutNodes() {
    return outNodes.iterator();
  }

  /**
   * Adds a directed edge to the graph.  The outNodes list of this
   * node is updated and the in-degree of the other node is incremented.
   *
   * @param node a <code>DigraphNode</code>.
   * @return <code>true</code> if the node was not previously the target of an edge.
   */
  public boolean addEdge(DigraphNode node) {
    if (outNodes.contains(node)) {
      return false;
    }

    outNodes.add(node);
    node.inNodes.add(this);
    node.incrementInDegree();
    return true;
  }

  /**
   * Returns <code>true</code> if an edge exists between this node
   * and the given node.
   *
   * @param node a <code>DigraphNode</code>.
   * @return <code>true</code> if the node is the target of an edge.
   */
  public boolean hasEdge(DigraphNode node) {
    return outNodes.contains(node);
  }

  /**
   * Removes a directed edge from the graph.  The outNodes list of this
   * node is updated and the in-degree of the other node is decremented.
   *
   * @return <code>true</code> if the node was previously the target of an edge.
   */
  public boolean removeEdge(DigraphNode node) {
    if (!outNodes.contains(node)) {
      return false;
    }

    outNodes.remove(node);
    node.inNodes.remove(this);
    node.decrementInDegree();
    return true;
  }

  /**
   * Removes this node from the graph, updating neighboring nodes
   * appropriately.
   */
  public void dispose() {
    Object[] inNodesArray = inNodes.toArray();
    for (int i = 0; i < inNodesArray.length; i++) {
      DigraphNode node = (DigraphNode) inNodesArray[i];
      node.removeEdge(this);
    }

    Object[] outNodesArray = outNodes.toArray();
    for (int i = 0; i < outNodesArray.length; i++) {
      DigraphNode node = (DigraphNode) outNodesArray[i];
      removeEdge(node);
    }
  }

  /**
   * Returns the in-degree of this node.
   */
  public int getInDegree() {
    return inDegree;
  }

  /**
   * Increments the in-degree of this node.
   */
  private void incrementInDegree() {
    ++inDegree;
  }

  /**
   * Decrements the in-degree of this node.
   */
  private void decrementInDegree() {
    --inDegree;
  }
}
